High-pressure sealing

ABSTRACT

In a high-pressure cylinder with an axial plunger, a seal assembly for scaling the gap between the cylinder wall and the plunger. The assembly is disposed in an annual recess in the wall having an open end and a bottom opposite thereto, and comprises a plunger-sealing ring, a cylinder-sealing ring, a resilient low-pressure ring, and an annual seal holder. The seal holder urges the plunger-sealing ring against the cylinder-sealing ring and the low-pressure ring, and urges the latter two rings against the recess bottom and against each other. The plunger-sealing ring and the cylinder-sealing ring are metallic, their mutual contact surfaces are fitted to each other, and the plunger-sealing ring has sufficient section modulus to ensure that under high pressure the contact and bending deformations at the mutual contact surfaces will be sufficiently small as to keep a tight fit therebetween.

FIELD OF THE INVENTION

[0001] This invention generally relates to methods of sealing a plungermoveable in a cylinder, and more particularly, in a high-pressurehydraulic cylinder.

BACKGROUND OF THE INVENTION

[0002] Pressing and extrusion under very high hydrostatic pressure is anefficient method of processing metals and other materials. Hydraulicpresses and cylinders of ever growing power are introduced in metalworking and other industries. High-pressure devices need seas capable towork under a wide range of pressures, from atmospheric pressure toextremely high pressures of 20-40 Kbar and more, at which the internaldiameter of the high-pressure cylinder expands by ˜1% and more.

[0003] A hydraulic cylinder has a cylinder wall with an open end whereina plunger enters the cylinder to compress a hydraulic liquid to highpressure levels. A seal assembly is disposed in an annular recess in thecylinder wall near the open end. Usually, a high-pressure seal assemblycomprises a high-pressure seal subassembly and a low-pressure sealsubassembly. With regard to expressions “high-pressure” and“low-pressure”, it will be understood by those skilled in the art that asingle pressure value cannot be specified as a border line between thetwo. What is meant here and further in the disclosure is, that from zeroor atmospheric pressure up to some intermediate pressure range, thesealing of the cylinder is provided solely by elements of the so-called“low-pressure subassembly”. At pressures higher than said intermediatepressure range and up to the maximal design pressure, the sealing of thecylinder is provided by the elements of the so-called “high-pressuresubassembly” only. In the intermediate pressure range, bothsubassemblies cooperate to provide sealing. Some elements of the sealingassembly may belong to both subassemblies.

[0004] Existing high-pressure seal assemblies usually include elementsmade of resilient material which, when interacting with the plunger andother metal parts, are subjected to rapid wear. Sometimes, parts of aseal assembly may require to be changed after each pressing cycle.

[0005] U.S. Pat. No. 3,606,356 to Beroset presents a high-pressure sealassembly disposed in a recess of a high-pressure cylinder wall. Thelow-pressure subassembly of U.S. Pat. No. 3,606,356 includes an annularTeflon ring with rectangular profile fitted on the plunger and placed inthe recess, an annular Teflon ring with triangular profile embracing therectangular ring and fitted to the recess outer wall, and a rubberO-ring inserted like a wedge between the two Teflon rings. Thehigh-pressure subassembly includes a metallic antiextrusion ring withtriangular profile spanning the recess radially, fitted on the plunger,and abutting the two Teflon rings from the open-end side of the recess.The seal assembly is closed by a retaining ring (seal holder) engaged ina screw-thread at the open end of the cylinder and biasing theantiextrusion ring against the two Teflon rings, thereby urging therectangular ring and the O-ring against the bottom of the recess. At lowpressures, the cylinder is sealed by the two Teflon rings and the O-ringbetween them. At high pressures, the rectangular Teflon ring and theO-ring cease to operate but the triangular Teflon ring expands under theaction of the pressure together with the cylinder wall, and the sealingis provided by the metallic antiextrusion ring in cooperation with thetriangular ring. Thus, the triangular Teflon ring actually belongs tothe high-pressure subassembly as well.

[0006] U.S. Pat. No. 3,865,387 discloses high-pressure seal assembliesincluding two metal rings disposed in a recess of the cylinder wallsimilar to that described above. In one embodiment, a metallic“plunger-sealing” ring with triangular profile is fitted to the plungerand sealingly abuts a seal holder fixed over the open end of the recess.A metallic “cylinder-sealing” ring of generally rectangular profile isfitted inside the recess of the cylinder wall, embracing the first ring,and also sealingly abutting the seal holder. The cylinder-sealing ringhas an internal skewed recess or bevel at the recess open-end side,accommodating part of the plunger-sealing ring, the two rings defining anarrow conical slit therebetween. The cylinder-sealing ring has two moreannular pocket-like recesses, each accommodating a rubber O-ring. Onerecess is at the beveled internal side opposite the edge of theplunger-sealing ring, and its O-ring is urged to the plunger-sealingring, to the cylinder-sealing ring, and to the plunger. The other recessis at the outer periphery of the cylinder-sealing ring and its O-ring isurged to the cylinder wall. Low-pressure sealing is provided by theO-rings only. High-pressure sealing is provided by the two metallicrings with the cooperation of the O-ring that is between them.

[0007] A second embodiment of the U.S. Pat. No. 3,865,387 has a similararrangement but the cylinder-sealing ring is beveled also at the recessbottom side. An annular groove is formed between the two metallic rings,accommodating an enlarged O-ring which is urged to both metallic rings,to the plunger and to the cylinder wall. Low-pressure sealing isprovided by the O-ring. High-pressure sealing is provided by the twometallic rings with the cooperation of the O-ring.

[0008] There are other high-pressure seal designs, where the operationof the high-pressure subassembly does not involve rapid wear of thelow-pressure subassembly, but then the high-pressure subassemblyexperiences too large elastic deformations leading to rapid wear.

[0009] Thus, U.S. Pat. No. 4,602,791 discloses a high-pressure sealassembly, where the high-pressure subassembly comprises a plurality ofelastic metallic rings with chevron profile (V-profile). The rings arestacked in a recess of the cylinder wall, embracing the plunger,abutting the plunger and the cylinder wall, with the V-profile opentowards the high-pressure side of the cylinder. Under the action of thehigh pressure, the V-profile opens elastically, following the expansionof the cylinder, and seals the gap around the plunger.

[0010] U.S. Pat. No. 4,787,642 discloses an arrangement, wherein anX-profile high-pressure metallic ring is disposed in a recess of thecylinder wall. Two deformable rings with triangular profiles are fittedin the lateral spaces of the X-profile, at the plunger and at thecylinder, respectively, constituting the low-pressure subassembly. Twometallic rings with wedge profiles are inserted in the upper and thelower spaces of the X-profile. The operation of this sealing assembly athigh pressure is the same as the previous one, the X-profile effectivelyworking as two opposite V-profiles.

SUMMARY OF THE INVENTION

[0011] In accordance with the present invention, it is provided ahigh-pressure seal assembly, where the high-pressure sealing is achievedby metallic rings only.

[0012] The seal assembly of the present invention seals the gap betweenthe cylindrical wall of a high-pressure cylinder and an axially moveableplunger. The seal assembly is placed in an annular internal recess inthe wall bounded radially by the cylinder wall, and axially by an openend and a bottom opposite thereto, and comprises a plunger-sealing ring,a cylinder-sealing ring, a resilient low-pressure ring, and an annularseal holder. The low-pressure ring is fitted on the plunger and isdisposed at the recess bottom, the cylinder sealing ring is disposed inthe recess around the resilient ring, and is tightly fitted against thecylinder wall, the plunger-sealing ring is tightly fitted on the plungerand is disposed in the recess extending radially along the cylindersealing ring and the low-pressure ring, the seal holder is inserted intothe open end of the recess, abuts the plunger-sealing ring, and istightened to the cylinder wall urging the plunger-sealing ring againstthe cylinder-sealing ring and the low-pressure ring, and urging thelatter two rings against the recess bottom and against each other. Boththe plunger-sealing ring and the cylinder-sealing ring are metallic,their mutual contact surfaces are fitted to each other, preferably bylapping, and the plunger-sealing ring has sufficient section modulus toensure that under high pressure the contact and bending deformations atthe mutual contact surfaces be sufficiently small as to keep a tight fittherebetween.

[0013] According to the design of the present invention, the metallicrings of the high-pressure subassembly are not subjected to significantbending deformations, and the resilient ring of the low-pressuresubassembly does not wear excessively under high pressure, therebyallowing for longer operational life and efficiency of the seal assemblyand operability at much higher pressures than the prior art seals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to understand the invention and to see how it may becarried out in practice, two embodiments will now be described, by wayof non-limiting example only, with reference to the accompanyingdrawings, in which:

[0015]FIG. 1 is a cross-section along the axis of a high-pressure sealassembly in accordance with the present invention.

[0016]FIG. 2 is a cross-section of the seal assembly of FIG. 2 withdeformations under high pressure shown schematically exaggerated.

[0017]FIG. 3 is a cross-section along the axis of a high-pressure sealassembly in accordance with a second embodiment of the presentinvention.

[0018]FIG. 4 is a cross-section of the seal assembly of FIG. 3 withdeformations under high pressure shown schematically exaggerated.

DETAILED DESCRIPTION OF THE INVENTION

[0019] With reference to FIG. 1, it is shown a high-pressure sealassembly 10 in accordance with the present invention, in a high-pressurecylinder 14 with wall 20, hydraulic working liquid 22 and plunger 24axially moveable into the cylinder to compress the working liquid. Theseal assembly is designed to seal the gap 26 between the wall 20 and theplunger 24, and is disposed in an annular internal recess 28 in the wall20, the recess being bounded radially by the cylinder wall and axiallyby an open end 32 and a bottom 34 opposite thereto. The seal assemblycomprises a metallic plunger-sealing ring 36, a metalliccylinder-sealing ring 40, a resilient low-pressure ring 42, an annularseal holder 44, and a supporting ring 46. The supporting ring 46 isdisposed at the recess bottom 34. It has no sealing function and can beregarded as part of the bottom 34 in the cylinder wall 20. The sealholder 44 is tightened axially by suitable means 48 to the cylinder wall20, thereby urging elements 36, 40, 42, and 46 of the seal assembly 10towards the recess bottom 34. The contact surfaces 50 of the seal holder44 and the plunger-sealing ring 36 have frusto-conical shape taperedtowards the open end 32, the mutual contact surfaces 52 of thecylinder-sealing ring 40 and the low-pressure ring 42 have alsofrusto-conical shape tapered towards the open end, while the contactsurfaces 54 between the metallic rings 36 and 40 are flat andperpendicular to the cylinder axis.

[0020] The resilient low-pressure ring 42 is tightly fitted on theplunger 24, along contact surfaces 55. The cylinder-sealing ring 40embraces the low-pressure ring 42 and is tightly fitted against thecylinder wall 20 along contact surfaces 56. In free state, thelow-pressure ring 42 has larger axial dimension than the ring 40, sothat when the seal is assembled, the ring 42 is elastically deformedunder the urging force of the seal holder 44, and thereby tightly fittedalso to the cylinder-sealing ring 40 along the contact surface 52. Theplunger-sealing ring 36 is tightly fitted on the plunger along a contactsurface 58. The mutual contact surfaces of metallic rings 36 and 40 arefitted very precisely to each other by lapping.

[0021] When the plunger 24 starts to move into the cylinder 14, thepressure in the hydraulic fluid 22 starts to rise from zero (oratmospheric) pressure. Up to some range of intermediate pressure values,the sealing of the cylinder is provided by the tight fit of thelow-pressure ring 42 to the plunger 24 along the contact surface 55, tothe cylinder-sealing ring 40 along the contact surface 52, and by thetight fit of the ring 40 to the cylinder wall 20 along the contactsurface 56. Thus, the rings 40 and 42 constitute a low-pressuresubassembly.

[0022] As the plunger 24 moves further into the cylinder 14, thehydraulic fluid pressure becomes higher and the cylinder experiencesconsiderable elastic expansion, as shown in exaggerated form in FIG. 2.The high pressure exerted thereby on the resilient low-pressure ring 42is transmitted to the cylinder-sealing ring 40 across the inclinedcontact surface 52 as an outward radial force which expands the ring 40together with the cylinder wall 20, thereby keeping the tight fit on thecontact surface 56. The high pressure also urges the cylinder-sealingring 40 to the plunger-sealing ring 36, making their fit along theprecisely lapped surfaces 54 fluid-tight. The axially directed pressureexerted by the cylinder-sealing ring 40 on the plunger-sealing ring 36is transformed, via of the inclined contact surfaces 50, into an inwardradial force which tightens the fit of the plunger-sealing ring 36 onthe plunger 24.

[0023] At pressures higher than the intermediate range and up to maximaldesign pressures, the sealing is provided only by the metallic rings 40and 36, across the contact surfaces 54, 56, and 58. Thus, theplunger-sealing ring 36 and the cylinder-sealing ring 40 constitute ahigh-pressure subassembly.

[0024] With the design of the present invention, the high pressure ofthe hydraulic liquid helps to tighten the fits that provide for thesealing effectiveness of the assembly. However, to achieve thistightening effect, the profiles of the metallic rings 36 and 40 musthave sufficient section moduli of resistance to ensure that, under highpressure, contact and bending deformations at the mutual contact surfacebe sufficiently small. This is especially important for theplunger-sealing ring 36 which spans the width of both rings 40 and 42,and is not precisely fitted to the seal holder 44 along the contactsurface 50. As seen in FIGS. 1 and 2, sufficient rigidity of the ring 36is ensured by its relatively thick profile, preferably with mean axialdimension at least equal to half radial dimension.

[0025] A second embodiment of a high-pressure seal assembly inaccordance with the present invention is shown in FIG. 3. The similarelements of the assembly are designated by the same reference numeralsas in FIGS. 1 and 2, the difference being that the recess 28 consists oftwo steps, the first step 28′, adjacent the open end 32, being of agreater diameter than the second step 28″. A shoulder 54′ is formedbetween the two steps. The second step 28″ is tapered towards the recessbottom 34, and correspondingly, the cylinder-sealing ring 40 is fittedto the cylinder wall along frusto-conical contact surfaces 56. Theplunger-sealing ring now rests on the shoulder 54′. Also, the contactsurfaces 54 between the plunger-sealing ring 36 and the cylinder-sealingring 40 are not flat and perpendicular to the common axis, butfrusto-conical, with taper towards the open end 32.

[0026] The sealing operation of the second embodiment in thelow-pressure range is the same as in the first embodiment. However, asshown in FIG. 4, under a high pressure the sealing action is enhanced.When the cylinder wall 20 expands due to the high pressure, thecylinder-sealing ring 40 expands under the radial force exerted by thehigh pressure on the surface 52. The ring 40 expands radially and slidesalong the precisely lapped contact surface 54 relative to theplunger-sealing ring 36. But due to the inclination of the surface 54,the ring 40 is pushed towards the recess bottom 34, thereby increasingthe tightness of the fit along the inclined contact surface 56. Also,since the ring 36 spans the rings 42 and 40 with an excess that rests onthe shoulder 54′, the profile of the ring 40 does not overhang the edgeof the ring 36 under high pressure, as is the case with the firstembodiment (compare FIG. 2 and FIG. 4). This overhang, at extremely highpressures, leads to extrusion of the material of the cylinder-sealingring into the gap between the plunger-sealing ring 36 and the cylinderwall 20 even though the ring is made of metal, and consequently to morerapid wear of the seal.

[0027] While there have been disclosed two preferred embodiments of theinvention, it is to be understood that changes may be made thereinwithout departing from the spirit of the invention. For example, therecess in the high-pressure cylinder wall may be formed by inserting achangeable liner into the cylinder. Also, the metallic high-pressuresealing rings may be composed of two or more rings each.

1. In a high-pressure cylinder with a wall, adapted to receive thereinan axially moveable plunger, a seal assembly for sealing the gap betweensaid wall and said plunger, comprising an annular internal recess insaid wall, the recess being bounded radially by the cylinder wall andaxially by an open end and a bottom opposite thereto, a plunger-sealingring, a cylinder-sealing ring, a resilient low-pressure ring, and anannular seal holder, wherein p1 the resilient low-pressure ring isfitted on the plunger and is disposed at the recess bottom; the cylindersealing ring is disposed in the recess around the low-pressure ring, andis tightly fitted against the cylinder wall; the plunger sealing ring istightly fitted on the plunger and is disposed in the recess, extendingradially along the cylinder sealing ring and the low-pressure ring; theseal holder is inserted into the open end of the recess, abutting theplunger-sealing ring, and being tightened to the cylinder wall to urgethe plunger-sealing ring against the cylinder-sealing ring and thelow-pressure ring, and to urge the latter two rings against the recessbottom and against each other; both the plunger-sealing ring and thecylinder-sealing ring being metallic, their mutual contact surfacesbeing fitted to each other, the plunger-sealing ring having sufficientsection modulus to ensure that under high pressure the contact andbending deformations at said mutual contact surfaces be sufficientlysmall as to keep a tight fit therebetween.
 2. A seal assembly accordingto claim 1, wherein said mutual contact surfaces of the plunger-sealingring and the cylinder-sealing ring are fitted to each other by lapping.3. A seal assembly according to claim 1 or 2, wherein high-pressuresealing of the gap between the plunger and the cylinder wall is providedentirely by said two metallic rings across the following interfaces:between the plunger and the plunger-sealing ring; between theplunger-sealing ring and the cylinder-sealing ring; and between thecylinder-sealing ring and the cylinder wall.
 4. A seal assemblyaccording to claim 3, wherein low-pressure sealing of said gap betweenthe plunger and the cylinder wall is provided by said resilientlow-pressure ring and said cylinder-sealing ring across the followinginterfaces: between the plunger and the resilient ring; between theresilient ring and the cylinder-sealing ring; and between thecylinder-sealing ring and the cylinder wall.
 5. A seal assemblyaccording to claim 4, wherein said interface between the resilient ringand the cylinder-sealing ring is a frusto-conical surface coaxial withthe cylinder and the plunger, and tapered towards the open end of therecess.
 6. A seal assembly according to any one of claims 1 to 5,wherein the plunger-sealing ring abuts the seal holder along a commonfrusto-conical surface coaxial with the cylinder and the plunger, andtapered towards the open end of the recess.
 7. A seal assembly accordingto anyone of claims 1 to 6, wherein said mutual contact surface of theplunger-sealing ring and the cylinder-sealing ring is an annular surfaceperpendicular to the cylinder axis.
 8. A seal assembly according toanyone of claims 1 to 6, wherein said mutual contact surface of theplunger-sealing ring and the cylinder-sealing ring is a frusto-conicalsurface coaxial with the cylinder and the plunger, and tapered towardsthe open end of the recess.
 9. A seal assembly according to claim 8,wherein the cylinder-sealing ring is fitted to the cylinder wall along acommon frusto-conical surface coaxial with the cylinder and the plunger,and tapered towards the bottom of the recess.
 10. A seal assemblyaccording to claim 9, wherein the recess in the cylinder wall comprisestwo steps, the one adjacent the open end being of larger diameter andaccommodating the periphery of the plunger-sealing ring, and the sealholder.
 11. A seal assembly according to any one of claims 1 to 10,wherein at least one of said metallic rings is made of bronze.
 12. Aseal assembly according to any one of claims 1 to 4, wherein at leastone of said metallic rings is made of steel.